1. Field of the Invention
The present invention relates to apparatus for laminating photoresist dry film onto circuit boards or panels that generally are made of copper and are used in the electronics industry, and more particularly, to a heated-roll laminator that is operative automatically simultaneously to laminate such film to both sides of each of a succession of stacked panels.
2. Description of the Prior Art
Photoresist dry films have been developed for use in the manufacture of printed circuit boards. Such boards have particular utility in the electronics industry. A particularly advantageous form of such film that is available commercially is the dry film photopolymer that is disclosed in U.S. Pat. No. 3,887,450, entitled "PHOTOPOLYMERIZABLE COMPOSITIONS CONTAINING POLYMERIC BINDING AGENTS". U.S. Pat. No. 3,887,450 was granted to Michael N. Gilano et al. and was assigned to Dynachem Corporation, 2631 Michelle Drive, Tustin, Calif. 92680. As manufactured, the film is characterized in being easily contaminated and also tacky and limp. Although tacky, the film is "peelable". This makes it possible to use a polyethylene cover film for protection and for facilitating handling. The composite is packaged in rolls. Typically, such photoresist dry films have thicknesses of 1.0, 1.5, 2.0 and 3.0 mils, and have widths in the range of 10 inches to 24 inches (25.4 cm. to 06.96 cm.).
Laminators for applying photoresist dry film to printed circuit boards have been proposed and used in the prior art. Prior art laminators, as manufactured and sold by Dynachem Corporation under its Model designations "120", "300", and "310", are manually operable laminators. Such laminators are useful in laminating one board or panel at a time. They require two supply rolls of photoresist dry film and two take-up rolls for disposing of the polyethylene cover film when a circuit board is to be laminated on both sides. Pull rolls are provided for pulling the photoresist dry film from each of the supply rolls over an associated side of the circuit board.
Aside from being manually operable and capable of laminating but one panel at a time, there has been a particular problem of undesirable film trim waste, particularly at the ends of the boards with such prior art laminators. This is because of an inherent difficulty in accurately positioning the leading ends of the films with respect to the leading end of the board as the films and the board are inserted between the pull rolls. As a consequence, it has been necessary to allow some excess or overlap of the films at the leading end of the board. Similarly, it has been difficult to accurately cut the films at the trailing end of the board, overlap again resulting. Thus, it has been necessary to trim both ends of the board.
Additional problems have been encountered in the use of the prior art laminators in applying photoresist dry films in wrinkle-free manner and uncontaminated condition to printed circuit boards. Such problems have stemmed from the presence of static electricity and film contaminating condensation resulting from smoke caused by the use of heated laminating rolls and heated devices used for cutting the film.
Machines for automatically assembling sheets of battery separator material over battery plates in envelope fashion and sealing the edges together have been proposed in the prior art. One such machine is disclosed in U.S. Pat. No. 4,080,727 granted to William H. Stolle et al. As described in the patent, "The material used for the separator envelope varies, but in general it must have some type of rib structure for holding most of its area away from the plate and it must be porous enough so that the acid and the ions can migrate in and out of the envelope from plate to plate."
In the patented machine, such ribbed separator material having a width greater than the battery plate to be enveloped is vertically fed by feeding rollers toward a folding station where it is cut by a shearing blade to a length of "about double" the height of the battery plate, a folding line also being scored across the material to facilitate bending thereof. A battery plate is conveyor fed against the fold line of the separator sheet, guides in the folding station causing the sheet to fold over and cover both upper and lower sides of the plate. Downstream, lifting devices lift the upper edge of the separator material on each side of the battery plate and hot melt adhesive is applied to the lower overlapping separator material edges. Rollers on each side of the conveyor press and seal the side edges of the envelope together. The sealed edges may then undergo a trimming operation. Assembled battery plates and envelopes are delivered from the downstream end of the conveyor onto a receiving platform from which they may be removed by hand or by a stacking storage device at the lower end of the platform which platform then is required to be downwardly inclined.
Other prior art patents that disclose machines for applying relatively stiff separators for producing enveloped battery plates are U.S. Pat. No. 2,373,082 granted to Carl G. Staelin and U.S. Pat. No. 4,026,000 granted to Kenneth A. Anderson.
In a preferred embodiment as disclosed in U.S. Pat. No. 2,373,082, pre-cut and creased mats of fibrous glass to be applied to the battery plates are arranged in a stack and fed between side edge guides, one by one, in horizontal position by grippers having sharp projections and by a linkage arrangement toward an applying station. Upon completion of movement in the feeding direction, the mat is only partially advanced to the applying station. When a succeeding mat is advanced, its leading edge abuts the trailing edge of the first mat between the side guides and pushes the latter to the applying station against a stop where the first mat is supported on a plate having a central slot located in alignment with the median and creased line of the mat. Here a battery plate delivered from a pasting machine is pushed vertically downward against the mat and through the slot in the plate so that the mat is folded over the opposite faces of the plate. Belts feed the plate downwardly pressing the mat in close contact therewith to cause the mat to be fixed securely to the plate. Upon emergence from the belts, the plates slide over a chute onto a conveyor. In a modified arrangement, the supply of mats is from a roll of fibrous glass web, the gripper having sharp projections feeding the web to the applying station in the same manner as the separate mats are fed in the preferred embodiment. At the applying station, the leading or advanced portion of the web is cut off to form a single mat.
U.S. Pat. No. 4,026,000 discloses apparatus for producing enveloped battery plates that is similar to the preferred embodiment disclosed in U.S. Pat. No. 2,373,082 in that a separator sheet dispenser is provided for dispensing individual separator sheets into an elongated passageway. The separator sheets, reaching a stopping point, buckle to form a fold at the approximate midpoint of the separator sheet. A battery plate dispenser feeds a battery plate against the fold line of the separator and compresses the sides of the separator against the opposite sides of the battery plate. Rollers feed the folded separator and battery plate through an ultrasonic sealing device for sealing the opposed edges of the separator to form an envelope around the battery plate.
U.S. Pat. No. 2,537,874 discloses a machine for producing display cards for jewelry and the like comprising a feeding rack for vertically feeding each of a succession of cards stacked in an upright position, adhesive applying rollers beneath the rack so that, as each cardboard passes downwardly, it receives adhesive material in strips on both sides thereof, and a horizontal sheet with an opening or slot therein underneath the rollers for supporting tissue paper. Each cardboard is adapted as it passes downwardly through the opening to engage the tissue paper and fold it against the side thereof, rollers being provided for pressing the tissue paper against the cardboard. The composite article is dropped into a container after which cards of appropriate size are cut by severing the article midway along the adhesive strips and transversely in accordance with the length desired for the display card.
U.S. Pat. No. 3,284,982 to John D. Conti discloses apparatus for banding cartons wherein the leading end of a carton being advanced by a pusher bar engages a downwardly extending portion at the leading end of a tape or ribbon of cellophane as supplied in between endless belts from a roll, jaws nipping the end of the tape and drawing it across the path of the oncoming carton. As the carton is moved over and above the tape, the leading end of the tape is pulled from the nipping jaws and heat sealed to the underside of the carton. As the carton is advanced, the tape is drawn up over the leading end and top side of the carton. The tape is then severed, allowing a length somewhat longer than enough to cover the trailing end of the carton, and the pusher bar advancing the carton is stopped. A vertically reciprocable tucker plate then tucks the tape around the trailing end of the carton and urges the severed end between the trailing end of the carton and a recessed portion of the adjacent pusher bar. The severed end of the tape is then said to be heat sealed to the underside of the carton.
While the foregoing prior art patents recognize some of the desirable attributes of laminators for making enveloped battery plates or display cards, there remain problems with adapting their teaching to an automatically operable laminator suitable for use in the efficient and effective lamination of easily contaminated and limp photoresist dry film to printed circuit boards or panels in a wrinkle-free and uncontaminated condition onto each of a succession of stacked printed circuit or other panels. Such problems include undesirable trim waste, mechanical difficulties in the handling of the panels which, when stacked upright in the manner of the prior art, tend to be unstable, mechanical problems in handling the film in wrinkle-free manner tending to result from the presence of static, and the contaminating effects on the film of condensation from smoke tending to result from the use of hot wire film cutting devices and from hot heated laminating rolls.